Copolymers from Castor Oil Prepolymers (COP). 4. Copolymerization of Methyl Methacrylate with COP

The copolymerization of castor oil prepolymer (COP) with methyl methacrylate (MMA) has been accomplished at 75°C using a free radical initiator. The monomer reactivity ratios of MMA (r₁) and COP (r₂) were determined to be r₁ = 3.04 and r₂ = 0.605. With an increasing concentration of COP in the binary mixture, copolymers with decreasing molecular weight were obtained. The copolymers obtained were powdery substances soluble in many organic solvents.     

Copolymers from Castor Oil Prepolymers (COP). 1. Copolymerization of Acrylonitrile with COP

The copolymerization of castor oil prepolymer (COP) was attempted with vinyl monomers in the presence of a free radical initiator at 75°C. It was found that acrylonitrile copolymerizes with COP in good yield, The copolymers were yellow brown in color and were soluble in hot dimethylformamide. The percentage composition of the copolymers was determined by the nitrogen of the copolymers. Their reactivity ratios were determined to be r₁ = 0.53, r₂ = 1.53.     

Trityl-initiated copolymerizations of propylene oxide with tetrahydrofuran. VIII. Influence of reaction parameters

The copolymerization of propylene oxide (PO) with tetrahydrofuran (THF) in dichloroethane (DCE) has been studied at ?10, 0, +10, and +20°C. The reactions were initiated by triphenylmethyl cations associated with the following gegenions: PF₆^?, SbF₆^?, and AsF₆^?. The overall energies of activation (E_α of PO and E_a of THF) obtained with the three gegenions increase as one passes from PF₆^? to AsF₆^? then to SbF₆^?, though the magnitude of the increase in each case is not substantial. On the other hand, the associated frequency factors A show a considerable variation with the gegenion. The bimodal distributions of the molecular weights, obtained by GPC with the copolymer produced from reactions initiated with triphenylmethyl hexafluorophosphate, show that the proportions of the lower molecular weight component (L) decrease as the solvent is changed from DCE to toluene, and this is even more marked when bulk polymerization conditions are adopted. The proportions of the higher molecular weight component (H) however increase, as does its molecular weight. The GPC molecular weight distributions of the copolymers initiated with triphenylmethyl hexafluorophosphate in DCE to which water has been added, show that the molecular weight of component H decreases with increasing concentration of water, while that of component L remains practically unchanged at a value of 308. This corresponds to an average degree of polymerization (DP ) of 4 to 5. The NMR and infrared spectra of copolymers prepared in the presence of still higher initial water concentrations indicate that the PO-based polymer segments are present in excess of those required for a 1:1 copolymer.     

Quasiliving Carbocationic Polymerization. XII. Forced Ideal Copolymerization of lsobutylene with Styrene

Forced ideal carbocationic copolymerization of isobutylene/styrene systems has been achieved by continuous addition of mixed monomer feeds to 2-chloro-2,4,4-trimethylpentane/TiCl₄ in n-hexane/methylene chloride charge by keeping the input rate equal to the overall rate of copolymerization. The composition of the copolymers was identical to that of the feeds over the entire monomer concentration range. The number-average molecular weight of the copolymers increased almost linearly with the amount of consumed monomers at higher isobutylene concentrations in the feed. The molecular weight increase was less pronounced at higher styrene concentration because more methylene chloride had to be used in the solvent system to keep the copolymer in solution. The micro-structure of the copolymers is uniform as determined by gel permeation chromatography (UV plus RI) and ¹³C-NMR spectroscopy According to these studies, true copolymers have formed. The probability of triads in the copolymer has been determined.     

Photoinduced optical anisotropy in azobenzene methacrylate block copolymers: Influence of molecular weight and irradiation conditions

The photoinduced anisotropy in a series of azomethacrylate block copolymers with different molecular weights and azo contents has been investigated under several irradiation conditions. Depending on molecular weight and composition, different microstructures (disordered, lamellar, spherical) appear, due to block microsegregation. Measurements of birefringence (Δn) induced with linearly polarised 488 nm light show that the highest (and stable) Δn_N values (birefringence normalised to the azo content) are achieved in copolymers with a lamellar structure. Lower Δn_N are obtained in the copolymers in which azobenzene units segregate to nano spheres and the lowest (and less stable) Δn_N values, appear in disordered systems not showing any defined microstructure. Besides, higher Δn_N is obtained in the copolymers with larger molecular weight of the poly (methyl methacrylate) and the azo polymer blocks, both in the microspheres segregated polymers as well as in those without a clear microstructure. This behaviour is consistent with that of the photoinduced order of azobenzene units obtained from dichroism measurements. Irradiation temperature (from 30 to 90 °C) and light power (from 100 to 500 mW/cm²) also influence the photoinduced response. Photoinduced Δn_N growth rate is faster when both temperature and irradiation power increase. Furthermore, birefringence is only induced at temperatures up to 90 °C, the maximum value being obtained at about 70 °C. No clear dependence of the final Δn_N value with light power has been found.     

Molecular structure of synthetic rubber. I. Light-scattering properties of styrene–butadiene copolymers

The discrepancy between the values reported for the weight-average molecular weight and molecular weight distribution of cold-type styrene-butadiene rubber is examined. The results obtained indicate that aggregation of the rubber due to hydrogen bonding or cluster formation is not a contributing factor to the high weight-average molecular weights obtained. The very broad molecular weight distributions, the M?_w/M?_n of the order of 10–20, are attributable to the presence of a few per cent of very high molecular weight fraction microgel in samples polymerized to moderate conversions. This microgel has been removed to various degrees by several methods: (1) mastication, (2) treatment with CaSO₄, (3) ultracentrifugation, and (4) ultrafiltration. The nature of this microgel is examined in terms of its light-scattering property, intrinsic viscosity, and concentrated solution viscosity. The weight-average molecular weight obtained by light scattering on these samples after removal of microgel are lower by as much as an order of magnitude. The operational definition of the weight-average molecular weight, M?′_w, is therefore introduced, corresponding to the one obtained after removal of the microgel. It is suggested that the actual and the operational weight-average molecular weights be used in conjunction in the characterization of these copolymers.     

Polymerization and copolymerization of trioxane: Factors influencing molecular weight and end groups

In bulk polymerization and copolymerization of trioxane with ethylene oxide, it has been shown that p-chlorophenyldiazonium hexafluorophosphate is a superior catalyst as compared to boron trifluoride dibutyl etherate (BF₃ · Bu₂O). Polymers and copolymers of significantly higher molecular weight have been obtained. The higher molecular weight has been attributed primarily to less inherent chain transfer during propagation, which in turn can be attributed to the superior gegenion PF₆^?. The polymerization proceeds via a clear period followed by sudden solidification. Faster polymerization and higher molecular weight polymers have been observed for homopolymerization than for copolymerization. The polymer yield obtained after solidification is determined by both rate of polymerization and rate of crystallization of polymers. These rates, in turn, are dependent on the catalyst concentration. The molecular weight is determined both by polymer yield and extent of inherent chain transfer. In the range of monomer to catalyst mole ration [M]/[C] = (0.5–20) × 10⁴ investigated, it has been found that in the higher range, the polymer yield is independent of the catalyst concentration and the extent of inherent chain transfer is inversely proportional to the half power of catalyst concentration: [M]/[C] = (0.5–8) × 10⁴ for homopolymerization and (0.5–3) × 10⁴ for copolymerization with 4.2 mole % ethylene oxide. In the lower range, the yield decreases with catalyst concentration and the extent of inherent chain transfer is inversely proportional to higher power of catalyst concentration. The dependence of molecular weight of polymers on catalyst concentration has been shown to be a complex one. The molecular weight goes through a maximum as the catalyst concentration is decreased. The maximum molecular weights have been obtained at [M]/[C] ≈ 8 × 10⁴ for homopolymerization and ～3 × 10⁴ for copolymerization with 4.2 mole % ethylene oxide. Prior to reaching maximum the molecular weight is inversely proportional to the half power of catalyst concentration indicating it is primarily controlled by inherent chain transfer. Upon further decrease of catalyst, molecular weight decreases as a result of both a decrease in polymer yield and an increase in inherent chain transfer. In copolymerization of trioxane and ethylene oxide, it has been ascertained that methylene chloride exhibits a favorable solvating effect. Although higher inherent chain transfer takes place in copolymerization than in homopolymerization, the extent of chain transfer is independent of ethylene oxide concentration. The difference in polymer yield and molecular weight a t different ethylene oxide concentrations is attributed primarily to the difference in k_p/k_t ratio. It also has been demonstrated that end capping of polymer chains can be accomplished by the use of a chain transfer agent—methylal.     

Synthesis and characterization of biodegradable homopolymers and block copolymers based on adipic anhydride

Homopolymers of adipic anhydride (AA) and block copolymers of ϵ-caprolactone (ϵ-CL) and AA have been synthesized with aluminum triisopropoxide as an initiator. Homopolymerization was studied at 20°C in toluene and methylene chloride (CH₂Cl₂). The end-group analysis agrees with a coordination insertion mechanism based on the acyl-oxygen cleavage of the AA ring. Living poly(ϵ-caprolactone) (PCL) chains are very efficient macro-initiators for the polymerization of AA, with formation of diblock copolymers of a narrow molecular weight distribution. At our best knowledge, low molecular weight ω-aluminum alkoxide PCL macroinitiators (M_n < 1000) allow the first valuable synthesis of PAA with a molecular weight as high as 58,000 and a quite narrow polydispersity (M_w/M_n = 1.2). Size-exclusion chromatography (SEC) and ¹³C NMR confirm the blocky structure of the copolymers, in agreement with DSC that shows two melting endotherms and two glass transitions characteristic of the crystalline and amorphous phases of PCL and PAA, respectively. Block copolymers of ϵ-CL and AA are also sensitive to hydrolysis, which makes them possible candidates for biomedical applications. Initiation of the AA polymerization in bulk with aluminum triisopropoxide in the presence of various ligands is also discussed. © 1997 John Wiley & Sons, Inc.     

Random Copolymers of 1,5-Dioxepan-2-one

ABSTRACT

Copolymers of 1,5-dioxepan-2-one (DXO) and e-caprolactone (?-CL), δ-valerolactone (δ-VL) or L-lactide (LLA) have been synthesized and characterized. High molecular weight copolymers were obtained using stannous-2-ethyl hexanoate as catalyst in bulk. Reactivity ratios for the copolymerization of DXO and δ-VL were determined at 110°C as r_VL=0.5 and r_DXO=2.3. At high conversion, depolymerization of δ-VL occurred, resulting in lower molecular weight and variations in the copolymer composition.

Physical properties, such as crystallinity and melting temperature of the DXO-copolymers proved to be strongly dependent on the choice of comonomer and on the molar composition of the copolymers. DXO appears to be incorporated into the poly-?-caprolactone (PCL) crystals and to some extent into the poly-δ-valerolactone (PVL) crystals, resulting in a more gradual decrease in crystallinity with increasing amount of DXO.     

Ethylene–propylene copolymerization with bis(β‐enaminoketonato) titanium complexes activated with modified methylaluminoxane

Ethylene–propylene copolymerization, using [(Ph)NC(R₂)CHC(R₁)O]₂TiCl₂ (R₁ = CF₃, Ph, or t‐Bu; R₂ = CH₃ or CF₃) titanium complexes activated with modified methylaluminoxane as a cocatalyst, was investigated. High‐molecular‐weight ethylene–propylene copolymers with relatively narrow molecular weight distributions and a broad range of chemical compositions were obtained. Substituents R₁ and R₂ influenced the copolymerization behavior, including the copolymerization activity, methylene sequence distribution, molecular weight, and polydispersity. With small steric hindrance at R₁ and R₂, one complex (R₁ = CF₃; R₂ = CH₃) displayed high catalytic activity and produced copolymers with high propylene incorporation but low molecular weight. The microstructures of the copolymers were analyzed with ¹³C NMR to determine the methylene sequence distribution and number‐average sequence lengths of uninterrupted methylene carbons. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5846–5854, 2006     

Quasiliving Carbocationic Polymerization. IX. Forced Ideal Copolymerization of Styrene Derivatives

Forced ideal carbocationic copolymerization of α-methylstyrene (αMeSt) with p-tert-butylstyrene (ptBuSt) and (αMeSt) with styrene (St) has been achieved by continuous monomer feed addition to a cumyl chloride/BCl₃ charge at -50°C by keeping the feeding rate of the monomer mixtures equal to the overall rate of copolymerization, The composition of the copolymers was identical to the composition of the monomer feeds over the entire concentration range. A quantitative expression has been derived to show that under forced ideal copolymerization conditions the composition of the copolymer can be controlled by the composition of the feed. Further, conditions have been found for forced ideal quasiliving copolymerizations, i.e., the number-average molecular weight of the copolymers increased almost linearly with the cumulative weight of consumed monomers by the use of suitably slow, continuous feed addition in the presence of relatively nonpolar solvent mixtures (60/40 v/v n-hexane + methylene chloride). In polar solvent (methylene chloride) the molecular weight increase was less pronounced due to chain transfer to monomer involving indane-skeleton formation; however, with charges containing large amounts of ptBuSt the molecular weight increase was surprisingly strong. Interestingly, ptBuSt does not homopolymerize in 60/40 v/v n-hexane/methylene chloride but it readily copolymerizes with αMeSt. This observation was explained by examining the relative rates of terminations of the cationic species involved. Conditions have been found for the pronounced quasiliving polymerization of St. In forced ideal quasiliving copolymerizations neither the molecular weights of αMeSt/ptBuSt or αMeSt/St copolymers nor the initiating efficiencies of the initiating systems used show a depression. The microstructure of representative αMeSt/ptBuSt copolymers obtained under forced ideal quasiliving conditions has been analyzed by ¹³C-NMR spectroscopy. According to these studies, true copolymers have formed and resonance peaks for various triads have been deduced.     

Chain transfer to solvent in BN 2-vinylnaphthalene radical polymerization

The synthesis of vinyl alcohol copolymers is limited due to the poor radical reactivity of vinyl acetate (VAc), the traditional precursor to polyvinyl alcohol (PVA). Main group monomers such as BN 2-vinylnaphthalene (BN2VN) have attracted attention as alternatives to VAc to form side chain hydroxyls via oxidation, but outstanding questions of molecular weight control remain. Herein we report systematic investigation of solvent, temperature, and initiator concentration as factors influencing BN2VN degree of polymerization. We find increased chain transfer to toluene, hypothesized to arise from differences in radical stabilization and reactivity by aromatic and BN aromatic rings. As a result of these combined efforts, high molecular weight (M_w ~ 10⁵ g mol⁻¹) BN2VN homopolymers and BN2VN-styrene copolymers were obtained.     

Novel synthesis of biodegradable star poly(ethylene glycol)‐block‐poly(lactide) copolymers

Biodegradable star‐shaped poly(ethylene glycol)‐block‐poly(lactide) copolymers were synthesized by ring‐opening polymerization of lactide, using star poly(ethylene glycol) as an initiator and potassium hexamethyldisilazide as a catalyst. Polymerizations were carried out in toluene at room temperature. Two series of three‐ and four‐armed PEG‐PLA copolymers were synthesized and characterized by gel permeation chromatography (GPC) as well as ¹H and ¹³C NMR spectroscopy. The polymerization under the used conditions is very fast, yielding copolymers of controlled molecular weight and tailored molecular architecture. The chemical structure of the copolymers investigated by ¹H and ¹³C NMR indicates the formation of block copolymers. The monomodal profile of molecular weight distribution by GPC provided further evidence of controlled and defined star‐shaped copolymers as well as the absence of cyclic oligomeric species. The effects of copolymer composition and lactide stereochemistry on the physical properties were investigated by GPC and differential scanning calorimetry. For the same PLA chain length, the materials obtained in the case of linear copolymers are more viscous, whereas in the case of star copolymer, solid materials are obtained with reduction in their T_g and T_m temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3966–3974, 2007     

Chain transfer studies of alternating copolymerization

Dimethylaniline (DMA) induces chain transfer in the zinc bromide-complexed donor–acceptor polymerizations of styrene–acrylonitrile to form alternating copolymers. The Mayo plots are linear, but the rates decrease with increase in DMA and degradative chain transfer occurs. Although conventional free-radical transfer agents have negligible effect on the rates or molecular weights, a twentyfold reduction of molecular weight is obtained with DMA. Spectroscopic data indicate the formation of an equimolar complex of DMA and ZnBr₂, but the lowering of molecular weight is not attributable to the reduction of the effective ZnBr₂, concentration. A possible mechanism involving a competition between [ZnBr₂(DMA)₂] and [ZnBr₂,DMA,AN] is suggested.     

Micellization through complexation of oppositely charged diblock copolymers: Effects of composition,polymer architecture,salt of different valency,and thermoresponsive block

The structural and electrical characteristics of polyelectrolyte complex micelles (PCMs) formed by mixing of oppositely charged double hydrophilic copolymers are studied by means of molecular dynamics simulations. In mixtures of linear diblock copolymers we found that the preferential aggregation number N_p of PCMs is a universal function of the ratio γ_± of the total positive to total negative charges of the mixture. The addition of divalent salts ions induces a secondary micellization. In mixtures of copolymers bearing a common neutral thermoresponsive block, micelles with contracted corona consisting of thermoresponsive blocks and complex polyelectrolyte core are formed at low salt concentration and temperature far away the biphasic regime. At high salt concentration and temperature in the biphasic regime, reversed micelles are obtained. In equimolar mixtures of linear copolymers with miktoarm stars we found that N_p of PCMs decreases as the number of charged branches of miktoarm copolymer increases. The shape of micelles progressively changes from spherical to worm-like with the increase of number of branches of miktoarm copolymers. Our findings are in full agreement with existing experimental and theoretical predictions and provides new and additional insights.     

Effect of the solvent upon the diffusion coefficient of polydisperse polystyrene and styrene-acrylonitrile copolymer in dilute solution

A laser homodyne spectrometer was used to obtain translational diffusion coefficients for dilute polystyrene and styrene-acrylonitrile copolymer solutions at room temperature. Data were obtained in the concentration range from 0.01 to 2.0 g polymer per 100 cm³ solution for polystyrene in benzene and in decalin; and for copolymer in dimethyl formamide, in methyl ethyl ketone, and in benzene. The samples were polydisperse polystyrenes of weight average molecular weights between 80,000 and 350,000 and polydisperse copolymers of weight average molecular weights between 200,000 and 800,000. The SAN copolymers were random copolymer samples containing 24% by weight acrylonitrile. For each of the systems investigated the concentration dependence of the diffusion coefficient was linear over the concentration range studied, and was expressed as D(c) = D₀(1+k_Dc). Values of D₀ could be explained with a modified Kirkwood-Riseman expression. Values of the parameter k_D obtained from the slopes could be interpreted using the two-parameter theory approach as suggested by Vrentas and Duda. The value of k_D is positive for high-molecular-weight polymers and negative for low-molecular-weight polymers. For a particular polymer, the molecular weight at which k_D changes sign is greater for poor solvents than for good solvents. Observed values of D₀ were 1 × 10^?7 to 7 × 10^?7 cm²/sec.     

Ring-opening metathesis polymerization of new α-norbornenyl poly(ε-caprolactone) macromonomers

Poly(ε-caprolactone) (PCL) macromonomers capped by a polymerizable norbornene end-group have been synthesized and (co)polymerized by ring-opening metathesis with formation of graft copolymers and polymacromonomers. α-Norbornenyl PCL macromonomers have been synthesized by ring opening polymerization (ROP) of ε-caprolactone (εCL) initiated by 2-diethylaluminoxymethyl-5-norbornene. Copolymerization of these PCL macromonomers with norbornene and polymerizable derivatives has been catalyzed by the [RuCl₂(p-cymene)]₂ PCy₃/(trimethylsilyl)diazomethane complex yielding a series of poly(norbornene)-graft-poly(ε-caprolactone) copolymers. These new graft copolymers have been characterized by a set of analytical methods, i.e., SEC, ¹H-NMR, FTIR, DSC, and TGA. Furthermore, PCL macromonomers have been polymerized into high molecular weight comb chains of narrow molecular weight distribution (M_w/M_n = 1.10) within high yields (90%). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2447–2455, 1999     

Flexibilized styrene‐N‐substituted maleimide copolymers. I. Multiblock copolymers prepared from styrene‐maleimide telechelics and polytetrahydrofuran

Telechelic copolymers of styrene and different N‐substituted‐maleimides (SMIs) with a molecular weight of 2000–8000 g/mol were synthesized using the starved‐feed‐reactor technique and were nearly bifunctional when the monomer feed had a high styrene concentration. The COOH‐terminated rigid SMI blocks were polycondensated with OH‐terminated poly(tetrahydrofuran) (PTHF) blocks, with a molecular weight of 250–1000 g/mol, which are the flexible parts in the generated homogeneous multiblock copolymer. The entanglement density, which is closely related to the toughness of materials, increased in these flexible SMI copolymers (ν_e = 5.2 · 10²⁵ m⁻³) compared to the unflexibilized ones (ν_e = 2.4 · 10²⁵ m⁻³). The glass transition temperature of these flexibilized, single‐phase multiblock copolymers was still high enough to qualify them as engineering plastics. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3550–3557, 2000     

A study of the molecular weights of tetrahydrofuran–propylene oxide copolymers by gel permeation chromatography and other methods

The cationic copolymerization of tetrahydrofuran and propylene oxide was studied in a batch system. Boron fluoride ethyl ether and 1,2-propanediol were used as catalyst—co—catalyst system. Number-average molecular weights M?_n of various copolymers were determined by vapor-pressure osmometry (VPO) and hydroxyl endgroup analysis (OH). The VPO and OH molecular weights differed considerably. To explain the differences, several copolymers were analyzed by gel permeation chromatography (GPC). The chromatograms obtained showed for each copolymer analyzed two peaks, one located in the high molecular weight region, the other in the low molecular weight region. An attempt is made to correlate the results and to show the usefulness of GPC in the characterization of THF—PO copolymers.     

Melting points of homogeneous random copolymers of ethylene and 1-alkenes

Melting points of copolymers of ethylene and 1-alkenes ranging from 1-butene to 1-octadecene have been determined. The copolymers were prepared by means of a homogeneous Et₃Al₂Cl₃/VOCl₃ initiating system so that in individual samples, comonomer contents do not vary with molecular weight. Evidence is presented for a random distribution of comonomer units in the copolymers. Melting points determined by differential scanning calorimetry are essentially independent of branch length at low comonomer contents. At higher comonomer contents (5–9 mol% 1-alkene), melting points decrease in the order 1-butene > 1-octene > 1-octadecene copolymers. The weight fraction of ethylene sequences drops to less than 60% in copolymers with 1-octadecene of high comonomer content and this results in a reduction in the crystallite thicknesses attained by these copolymers.